Dark Ammonium Assimilation Reduces the Plastoquinone Pool of Photosystem II in the Green Alga <i>Selenastrum minutum</i>

Mohanty, N.; Bruce, Doug; Turpin, David H.

doi:10.1104/pp.96.2.513

Cited by 16 publications

(7 citation statements)

References 21 publications

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“…At each instrument light intensity setting (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12), the intensity of the measuring beam is increased by an average factor of 60.11 between 1.6 and 100 kHz; this is close to the expected increase of 62.50 (100/1.6 kHz). However, Table I also indicates that as one progresses to higher instrument light intensity settings, the increase in intensity at 1.6 kHz is slightly larger than the increase at 100 kHz; this results in the decrease in the ratio of light intensity at 100 to 1.6 kHz at higher intensity settings.…”

supporting

confidence: 62%

Limitations of the Pulse-Modulated Technique for Measuring the Fluorescence Characteristics of Algae

Ting¹,

Owens²

1992

Plant Physiol.

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Precise measurements of the minimal fluorescence yield (F.) and maximal fluorescence yield (Fm) of a dark-adapted sample are prerequisites for the quantification of other fluorescence parameters. The pulse amplitude-modulated chlorophyll fluorometer (PAM 101 Chlorophyll Fluorometer, Heinz Walz, Effeltrich, Germany) and saturating pulse technique have frequently been used in measuring F. and Fm and in resolving the contributions of photochemical and nonphotochemical quenching to the total fluorescence yield. The extent to which instrument-dependent factors may affect the accurate measurement of F. and Fm is addressed. It is shown that the increase in pulse amplitude-modulated measuring beam intensity at 1.6 and 100 kHz was nonlinear at higher light intensity settings. The implications of this for measurements of F. (1.6 kHz) and Fm (100 kHz) are discussed. It is also demonstrated that underestimation of Fm may result due to saturation of the PAM 101 photodiode by scattered infrared light associated with intense light pulses. In addition, it is shown how sample-dependent factors may affect measurements of F. and Fm in samples with low chlorophyll concentrations, in particular, dilute algal suspensions of Phaeodactylum tricornutum and Chiamydomonas reinhardtii. A technique is presented for the accurate measurement of F. in algal suspensions (<8 gg chlorophyll a mL-1). The importance of examining the saturating pulse transient and Fm level as a function of the damping setting, pulse width, and pulse intensity, and in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea is discussed.The quantitative analysis of Chl a fluorescence quenching has provided information on processes that may be regulating PSII photochemistry during steady-state photosynthesis (7,13,16,19 tion of the primary quinone acceptor (closed trap), photochemical quenching of excited states is eliminated (qp = 0) and the fluorescence yield is maximal. When all reaction centers are capable of photochemistry, qp is maximal (=1) and the fluorescence yield is low. In contrast, a diverse group of components contributes to qN; these essentially reflect the nonphotochemical pathways by which excited states in the antenna can be deactivated. The primary component involves thermal deactivation of excited states and is associated mainly with the establishment of the transthylakoid pH gradient during electron transport and possibly with the xanthophyll cycle (2, 12). Other qN components include state transitions and photoinhibition (4,6,9,15). The extent to which each component contributes to the total amount of qN measured depends on the history of the sample and the conditions under which the measurements are conducted (10, 13).Utilization of the PAM Chl fluorometer (PAM 101 Chlorophyll Fluorometer, Heinz Walz, Effeltrich, Germany) (16) and the saturating light pulse (light-doubling) technique (1) have proven useful in resolving the contributions of both qP and qN to the fluorescence yield observed under different physiological conditions. Th...

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supporting

confidence: 62%

Limitations of the Pulse-Modulated Technique for Measuring the Fluorescence Characteristics of Algae

Ting¹,

Owens²

1992

Plant Physiol.

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“…1B), thus implying that the PQ pool is in a predominantly reduced state during darkness. In addition, the¯uorescence decay kinetics after a saturating¯ash, used as a measure of the dark re-oxidation of the primary electron acceptor Q A (Schreiber 1986;Mohanty et al 1991;Govindjee et al 1992), was retarded in WP needles (Fig. 5, Table 2), thus indicating that indeed Q A is in a more reduced state in WP.…”

Section: Discussionmentioning

confidence: 97%

“…Although the precise mechanism(s) of non-photochemical reduction of the PQ pool is still a matter of intensive research (Mohanty et al 1991;Asada et al 1992Asada et al , 1993Groom et al 1993;Field et al 1998) it is generally assumed that stromal components are the main source of reducing equivalents feeding the photosynthetic electron transport chain with electrons during darkness. The data summarized in Table 1 show that the apparent size of the stromal electron donor pool to PSI is much higher (5-fold) in WP needles.…”

Section: Discussionmentioning

confidence: 99%

Photosynthetic electron transport adjustments in overwintering Scots pine ( Pinus sylvestris L.)

Ivanov

Sane

Zeinalov

et al. 2001

Planta

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As shown before [C. Ottander et al. (1995) Planta 197:176-183], there is a severe inhibition of the photosystem (PS) II photochemical efficiency of Scots pine (Pinus sylvestris L.) during the winter. In contrast, the in vivo PSI photochemistry is less inhibited during winter as shown by in vivo measurements of deltaA820/A820 (P700+). There was also an enhanced cyclic electron transfer around PSI in winter-stressed needles as indicated by 4-fold faster reduction kinetics of P700+. The differential functional stability of PSII and PSI was accompanied by a 3.7-fold higher intersystem electron pool size, and a 5-fold increase in the stromal electron pool available for P700+ reduction. There was also a strong reduction of the QB band in the thermoluminescence glow curve and markedly slower Q-A re-oxidation in needles of winter pine, indicating an inhibition of electron transfer between QA and QB. The data presented indicate that the plastoquinone pool is largely reduced in winter pine, and that this reduced state is likely to be of metabolic rather than photochemical origin. The retention of PSI photochemistry, and the suggested metabolic reduction of the plastoquinone pool in winter stressed needles of Scots pine are discussed in terms of the need for enhanced photoprotection of the needles during the winter and the role of metabolically supplied energy for the recovery of photosynthesis from winter stress in evergreens.

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“…Dark NH/ assimilation by etiolated plants exposed to external C-deprivation probably influenced carbon metabolism by stimulating glycolysis and mitochondrial respiration (Mohanty et al, 1991) to provide carbon skeletons and A TP/NAD(P)H requirements of NH 4 + assimilation.…”

Section: "Light and Dark" Nh/ Assimilationmentioning

confidence: 99%

15n NMR Spectroscopic Study of Ammonium Ion Assimilation by Spirodela Oligorrhiza—lemnaceae—as Affected by Light and Carbon Supply in Green and Extoliated Plants

Monselise

Kost

1998

Israel J Plant Sci

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This article is dedicated to the memory of my father, Professor Shaul Paul Monselise, a decade after his departure.ABSTRACT Nitrogen assimilation and amino acid production in Spirodela oligorrhiza plants exposed to 30 mM 15 NHFI was studied using 15 N NMR spectroscopy. Green and etiolated plants were studied under different light regimes and in the presence of added carbon, either as sucrose or as a-ketoglutarate. Etiolated plants are capable of ammonium assimilation and, as in green plants, this occurs via the glutamine synthetase/glutamine oxoglutarate amine transferase (GS/GOGAT) and the aspartate aminotransferase/asparagine synthetase pathways. The major assimilation products in both etiolated and green plants were glutamine and asparagine. Thus our results confirm that N-amides are key detoxification products when plants are exposed to external ammonium ion, and act as storage reservoirs or sinks for assimilated ammonium. In plants grown under continuous light, ammonium ion was taken up and assimilated to completion. L-methionine DL-sulfoximine, a GS inhibitor, inhibited ammonium ion assimilation but not its uptake. Addition of azaserine, a GOGA T inhibitor, resulted in the disappearance of a-amino signals, and 15 N incorporation into the glutamine amide-N position only. This is evidence for the operation of the GS/GOGAT pathway, as opposed to the glutamate dehydrogenase (GDH) pathway, in both green and etiolated plants. Even in the dark and under various stress conditions, no sign of ammonium ion assimilation via the GDH pathway could be detected.The amount of amino acid metabolites strongly depended on the light regime and the extent of external carbon supply. Supply of a-ketoglutarate to the etiolated plants increased ammonium ion uptake and assimilation. Ornithine and arginine were also formed, consistent with the operation of the ornithine cycle.

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Dark Ammonium Assimilation Reduces the Plastoquinone Pool of Photosystem II in the Green Alga Selenastrum minutum

Cited by 16 publications

References 21 publications

Limitations of the Pulse-Modulated Technique for Measuring the Fluorescence Characteristics of Algae

Limitations of the Pulse-Modulated Technique for Measuring the Fluorescence Characteristics of Algae

Photosynthetic electron transport adjustments in overwintering Scots pine ( Pinus sylvestris L.)

15n NMR Spectroscopic Study of Ammonium Ion Assimilation by Spirodela Oligorrhiza—lemnaceae—as Affected by Light and Carbon Supply in Green and Extoliated Plants

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